There is no single universally accepted “exact” definition. The most commonly used clinical-pathologic convention is:

Thus, the practical distinction is same quadrant/region = multifocal; different quadrants/regions = multicentric. The NCI describes multicentric breast cancer as more than one independently formed tumor, likely in different quadrants of the breast, while a patient pathology resource uses the same quadrant versus different quadrants distinction (NCI definition; Breast Cancer Now pathology guide).

A precise report should state the number of invasive foci, their sizes, sites/quadrants, and the measured distance between them, because terminology and the 5-cm cutoff vary across studies. This inconsistency is recognized in the literature.

No. They do not have to be the same histologic type to be called multifocal or multicentric.

The terms describe the anatomic distribution of separate synchronous malignant foci in one breast, not whether the foci match microscopically:

For example, an invasive ductal carcinoma focus plus a separate invasive lobular carcinoma focus in the same breast can still be multiple ipsilateral disease, usually reported as multifocal or multicentric according to location.

However, pathologists should assess and report each distinct focus where relevant because they can differ in:

A discordant focus can affect systemic-treatment planning. In routine practice, multiple foci are often biologically similar, but heterogeneity occurs, so “same tumor type” is not a defining requirement. A recent review also characterizes multifocal/multicentric disease broadly as multiple synchronous tumor foci in the same breast, rather than requiring an identical histotype (recent review).

Your credits are exhausted. You can purchase a top-up or subscribe to a plan to continue using Orris. If you're already subscribed, your daily credits will reset tomorrow.